Question

The initial ratio of sugar to flour in a dough was 2: 7. To 9 kg of the dough John added more sugar to make the sugar to flour ratio 2: 5. How much sugar did John later add?

Answer 1

Given the ratio 2:7

then 9 Kg of dough will contain

$\frac{2}{9}. 9 = 2 kg of sugar$

$\frac{7}{9}.9=7kg of flour$

Lets suppose x kg of sugar is added to the dough

then the total dough would be 9+x

The quantity of sugar = 2+x kg

The quantity of flour = 7 kg

The ratio = 2:5

so we have the ratio for sugar

$\frac{5}{7}.(9+x)=7 kg$

$5(9+x)=7.7$

$45+5x=49$

$5x=49-44$

5x=4

x=0.8kg

Hence 0.8 kg of sugar is added to make the ratio 2:5

Answer 2

this question was asked in rrb alp 13th aug 2018 2nd shift.

initial ratio of sugar :  flour is then final ratio sugar :  flour

                          2    :         7                                2     :     5

according to question flour remains same but amount of sugar is added

we  will make the quantity of  flour equal either side

                2*5=10       :   7*5=35                        2*7=14   :  5*7=35

now we can equate , from initial to final their is increase of 10 to 14 change of 4 unit.   {9/35+10}*4= 4/5 kg will be the answer.